This is an openCart configuration issue. Changing the DocumentRoot will result in wrong asset urls so your css, js and image files could not be find. OpenCart still expects the old path.If you cannot solve this issue with this amount of information, please ask at an OpenCart support channel how to solve this issue.

best wishes,Altrea

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This is also a general issue - you MUST NOT change DocumentRoot AFTER installing any Software in htdocs. This results in different URLs for the same document and may cause several problems. If you want to run your software from a different DocumentRoot, FIRST change DocumentRoot and THEN install the related software.